The design of fluidization grids for fluidized polymerization reactors is known in the art and disclosed in such patents as U.S. Pat. No. 4,933,149 and EP Patent 173,261. Mechanically swept distribution grids are described in U.S. Pat. No. 3,254,070 to Roulen. A process with no distributor plate is described in U.S. Pat. No. 3,023,203 to Dye which allows the largest particles to fall through and melt in an extrusion zone.
U.S. Pat. No. 3,300,457 to Schmid et al. discloses an elaborately designed stirrer which extends from the base of the reactor to the top of a constant diameter reaction zone, this system also does not include a distribution grid to disperse the fluidizing gas. Moreover, the upper bound on suitable fluidization velocities of 0.5 ft/sec (0.18 m/sec) is much lower than the desirable velocity of utility in a commercial fluidized bed polymerization.
Reactors with multiple individual reaction zones are known. For example, U.S. Pat. No. 4,390,669 teaches staged type reactors, however an additional suspension zone stage between the reactors in a hydrocarbon diluent is required for the improvements described. These reactors generally require, however, multiple reaction systems to attain the desired product properties and none teach how to achieve controlled residence time within one reactor.
U.S. Pat. Nos. 3,957,448 and 5,378,434 disclose "staged" reactors contained within a separate pressure vessel, however both of these require use of a horizontal, mechanically agitated bed for operation.